The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2001-019120 filed on Jan. 26, 2001 the entire contents thereof is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a drive unit for a prosthetic limb, which unit is adapted to move a prosthetic limb such as a prosthetic arm or a prosthetic leg with a power.
2. Description of Background Art
A hydraulic type drive unit for a prosthetic limb is disclosed in Japanese Patent Publication No. Sho 62-13017. A linear motor type drive unit is disclosed in Japanese Patent Laid-open No. Sho 63-3855. A pneumatic type drive unit is disclosed in Japanese Utility Model Laid-open No. Sho 63-102420.
In the case of adopting a prior art drive unit of any one of the above-described types it is necessary for a battery to be used as a power source for the drive unit. With respect to the use of a battery, since an energy density of the existing battery is as small as about 50 to 100 wh/kg, the battery fails to satisfy the operation of the drive unit for a long time. To cope with such an inconvenience, it may be considered to make use of power generated by an internal combustion engine. However, the use of an internal combustion engine is disadvantageous in terms of exhaust noise, oscillation, etc.
In view of the foregoing, the present invention has been made. It is an object of the present invention is to provide a new drive unit for a prosthetic limb, which is capable of driving a prosthetic limb with comfort for a long time.
To achieve the above object, according to a first feature of the present invention, there is provided a drive unit for a prosthetic limb, adapted to bendably/stretchably drive first and second prosthetic limb bodies, which are connected to each other via a joint, relative to each other. A Stirling engine includes a displacer unit mounted at an arbitrary portion other than the prosthetic limb bodies and a power cylinder unit mounted between the prosthetic limb bodies for bending/stretching the prosthetic limb bodies relative to each other. A compression chamber of the displacer unit is connected to an operation chamber of the power cylinder unit via a flexible pressure conduit. A combustor for heating an expansion chamber disposed in a displacer cylinder of the displacer unit is provided around a head portion of the displacer cylinder. Fuel supply means are operatively connected to the combustor. An actuator is provided for arbitrarily driving a displacer piston of the displacer unit that is connected to the displacer piston. It is to be noted that the first and second prosthetic limb bodies correspond to a thigh portion 2 and a shank portion 4 constituting a prosthetic leg, respectively and the fuel supply means corresponds to a fuel cartridge 38 in an embodiment of the present invention to be described later.
With this first feature, a bending/stretching speed of the second prosthetic limb body relative to the first prosthetic limb body can be controlled from zero to an arbitrary value by controlling an operational speed of the displacer piston from zero to an arbitrary value by means of the actuator. As a result, the prosthetic limb can be moved on the basis of the user""s intention.
Since the combustion form in the combustor of the displacer unit is continuous combustion, it is possible to enhance a combustion efficiency and to eliminate any combustion oscillation. In addition, since the fuel supply means is adopted, it is possible to bendably/stretchably drive the prosthetic limb for a long time.
Since only the power cylinder unit is provided on the prosthetic limb bodies and the relatively heavy displacer unit and the fuel supply means are disposed at arbitrary portions other than the first and second prosthetic limb bodies, it is possible to make both the prosthetic limb bodies lightweight and slim while ensuring a smooth bending/stretching motion of both the prosthetic limb bodies.
According to a second feature of the present invention, a hydraulic converter for converting a pressure in the compression chamber into a hydraulic pressure and transmitting the hydraulic pressure to the operation chamber of the power cylinder unit is provided between the compression chamber and the pressure conduit.
With this second feature, since a pressure in the compression chamber of the displacer unit is converted into a hydraulic pressure by the hydraulic converter, and the hydraulic pressure is transferred to the operation chamber of the power cylinder, it is possible to eliminate the occurrence of elastic compression, which has been caused by a working gas, in the pressure conduit and the operation chamber, and hence to improve a pressure transmission efficiency.
According to a third feature of the present invention, power generating means driven by a second Stirling engine is connected to both a storage battery and an electronic control unit for controlling the actuator. It is to be noted that the power generating means corresponds to a power generating coil 73 in the embodiment of the present invention to be described later.
With the third feature, since the power generating means is operated by the second Stirling engine and thereby the storage battery is usually, automatically charged with sufficient electricity, the electronic control unit and the actuator can be normally operated by means of the storage battery. As a result, it is possible to operate the power cylinder unit for a longer time.
According to a fourth feature of the present invention, the displacer unit and the actuator are mounted on a belt worn by a user.
With the fourth feature, a user can easily, rapidly, and simply mount/dismount the displacer unit by mounting/dismounting the belt on a user""s body.
According to a fifth feature of the present invention, the first and second prosthetic limb bodies are taken as a thigh portion and a shank portion constituting a prosthetic leg, respectively, and the displacer unit is contained in a hollow portion of a foot portion joined to a lower end of the shank portion.
With the fifth feature, it is possible to dispose the displacer unit by making effective use of a dead space in the foot portion of the prosthetic leg.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.